Hyper-Methylation DAZAP2 May Suppress Its Expression in Specific Subtypes of Myeloma.

Abstract 4421

Most malignant features of cancer cells are triggered by activated oncogenes and the loss of tumor suppressors due to mutation or epigenetic inactivation. We previously reported that DAZAP2 was down-regulated in newly diagnosed myeloma (MM) and this may influence MM cell growth and survival. This study was undertaken to evaluate the mechanism of down-regulation DAZAP2 and determine the methylation status and loci of its promoter by using bisulphite genomic-sequencing (BGS) method in KM3 myeloma cell line. Two islands with rich GC box in the promoter of DAZAP2 gene were identified and amplified by using bisulfite-sequencing PCR (BSP). Island 1 spans -472 to -247 including 9 CpG sites (CpGs) and island 2 covers -226 to -13 including 23 CpG sites. The ratio of methylated CpGs in two CpG islands was 46.25%. The above sequences were demethylated and inserted into a pGL2-basic vector. COS-7 cells were transfected with recombinant plasmids and the activity of luciferase was evaluated. The results showed that the CpG island 1 had a weakly transcriptional activity, whereas the CpG island 2 had a strong transcriptional activity (2.38 folds compared with the positive control). The other sequence which covered CpG island 1 and 2 showed a remarkable activity (15.1 folds compared with the positive control). These data indicated that CpG island 2 of DAZAP2 gene may be hypermethylated and suppressed its expression in MM cells. We further correlated DAZAP2 expression with normal plasma cells and malignant myeloma cells, as well as the molecular subtypes which the dataset includes 8 genetic subtypes (MY, PR, LB, MS, HP, CD-1, CD-2, and MF) from 351 newly diagnosed myeloma cases (Zhan, 2006). Interestingly, we extended and confirmed our previous discovery that DAZAP2 was significantly down-regulated in MM cells by using a large uniform dataset (P = 0.004). The low expression of DAZAP2 was especially significant in the subgroups of MY, PR, LB, HP, and CD-1. This study warrants further investigation of DAZAP2 and its potential role in myeloma.